Keri Russell lies half-naked on a bed at a soundstage in the Gowanus section of Brooklyn. Dressed in a black bra and stockings, her pencil skirt hiked up above her waist, she’s smiling, which is surprising given that in the past half hour, she’s been spanked on her naked rear or whipped with a belt more than 50 times.

Russell is filming the fifth episode of “The Americans,” FX’s new drama about Soviet spies in America in the early 1980s. As Elizabeth Jennings (her American name) Russell is undercover, using sex as a weapon in the soon-to-be-lost battle against capitalist oppression. This scene calls for Elizabeth’s mark, a corporate surveillance executive with a penchant for harmful sexual play, to turn unexpectedly violent.

The mechanics of the scene are tricky. After a kiss with guest-actor John Dossett, the two fall to the bed for a quick bout of fake sex. Dossett then flips Russell over, slaps her bottom twice and repeatedly whips her with a belt. Russell’s character realizes what’s happening, screams and squirms away.

In a scene of this sort, there are many details to work out. How many buttons should be undone on her peach blouse before Dossett removes it? When should Russell reach for his belt, and how long should her hands be down there? Then, when and how should he reach for the fake-leather belt which, in a true piece of showbiz magic, makes exactly the sound of a belt slashing flesh without causing Russell any pain?

Throughout, one is struck by Russell’s nonchalance. But the accompanying remarks, as heard on headphones while the scene is filmed, would constitute highly inappropriate behavior in any other workplace.

“If you want me to do the full unzipping, it’s gonna take a little time,” says Russell.

And then a crew member chimes in: “I feel like such a pervert watching this.”

As the scene progresses, one thing becomes abundantly clear: Keri Russell has come a long, long way since “Felicity.”

On a short break, the 36-year-old actress, now covered in a plush blue robe, relishes a quick snack.

“I’ve had a burrito and some chocolate. I feel great,” says Russell. “I’m ready to get naked again.”

In “The Americans,” Russell’s Russian-born spy was recruited by the KGB as a teen, and paired with Rhys’ Philip (they are instructed not to share their real names with each other) to become a husband and wife in America, have kids, and pose as a regular family while secretly carrying out missions for the motherland.

As such, “The Americans” is infused with action and lust, as the pair employ sex when needed, and also indulge in some primo ass-kicking, including Russell sending a man’s head through a wall in the first episode.

“One of my favorite shots in the pilot comes when she back-fists her own husband,” says show creator and ex-CIA man Joe Weisberg. “There are scenes coming up where you see her turn into this cold-blooded killer, and then go back in the next scene to being this warm mother. Her capacity to go back and forth between the two so naturally is what blows me away.”

The timing of the show could have seemed precipitous, as Russell had just given birth to her second child, daughter Willa Lou before production started (she and her husband, Shane Deary, also have a son, River Russell, now 5).

“I had just had a baby. I was nursing, and then going and punching people,” she says. “It was so weird.”

But while she filmed the pilot barely four months after giving birth — the veteran dancer says she did little training, as when it comes to being in shape, she’s “lucky on that front” — she says the nature of the Jennings’ relationship made the show too intriguing to pass up.

“I was just so interested in that marriage,” she says. “I thought, where are they gonna go with this? It was so smart, and so far from a normal procedural that I thought, this could be something.”

In the first episode, we learn that almost two decades and two children (Paige, 13, and Henry, 10) into their arranged marriage, Philip is far more in love with Elizabeth than vice versa, and also far more taken with their new country. This blend of personal and professional tension between the two will drive much of the plot.

“Philip is getting to a point where he knows this isn’t a sustainable lifestyle,” says Rhys, the Welsh actor who previously co-starred in ABC’s “Brothers and Sisters.”

“By the second episode, you realize there are elements to their missions that are getting dangerous. He realizes the net is closing. They can get sentenced to death, or what, they get sent back to Russia and take the kids to Moscow? It’s not a viable option anymore.”

Elizabeth, however, feels differently. We also learn in Episode 1 that she has suffered greatly for the cause — especially due to some brutal abuse at the hands of a KGB superior — and so to abandon it now would seem to discard all she’s been through.

“I just think it’s black-and-white to her. She believes there’s a right way and a wrong way,” says Russell. “Plus she’s given up everything. For this to go badly now, it would be such a waste.”

Rhys believes that his character’s growing love of America, as well as the couple’s ever-changing and challenged relationship, will allow viewers to root for them as they do for some of television’s other notorious antiheroes, even while the couple works to bring our country down.

“In ‘Homeland,’ you find yourself rooting for Brody, and then you go, hang on a minute,” says Rhys. “And with ‘Breaking Bad,’ you give Walter White an incredibly human justification. He’s dying of cancer, so you’re with him. Immediately, you’re like, ‘Whatever it takes.’”

Time will tell if audiences warm to these enemies of America, but there’s probably no one rooting for its success harder than Russell, a Boerum Hill resident who’s practically shooting in her own backyard.

When she agreed to do the show, she knew that it would either be shot within in walking distance from her Brooklyn home, or in Yonkers.

“The creator also lives in Brooklyn, but we didn’t know if we could get this,” she says of the soundstage at Eastern Effects Studios. “I was begging for it to be in Brooklyn. I just didn’t know my dream was gonna come true.”

Whether “The Americans” becomes a dream come true for FX remains to be seen. But whatever the show’s fate, those who do watch are likely to come away with a very different impression of this fresh-faced girl next door.

“I think it’s brilliant, brave casting,” says Rhys. “If you look at her, you don’t think [she’s a] KGB operative. You don’t go, she’ll kick a man’s head through a wall. She’s this little pistol, and given her track record, this turns America’s perception of her on its head.”